shows that while the sulphocyanide naturally present in the serum is capable of combining with added iron, the serum possesses the power of preventing the formation of sulphocyanide of iron when both compounds are added and intermixed with it.

An analogous masking of chemical action is described by Bernard. He found that when a solution of lactate of iron is mixed with serum, and a solution of cyanide of potassium is then added, prussian blue is not formed, as would be the case if the solutions were mixed in water instead of serum.

I have not been able to decide positively whether the sulphocyanide is or is not confined to the serum. Analysis, after combustion, is unsuitable, because sulphocyanides are formed in the combustion of organic matter. But so far as I have been able to determine from the maceration of the clot in water, the sulphocyanides exist only in the serum.

The foregoing facts point either to the presence of free sulphocyanic acid, or of sulphocyanide of potassium, or sodium, or of both, in the serum of the blood. This leads to the consideration of that much-vexed question, the cause of the red colour of the blood. So far as concerns exact colour, nothing more closely resembles blood than a solution of sulphocyanide of iron. This is prima facie evidence that red blood owes its colour to the iron compound. The iron is known to be localized in the globules. These are surrounded by a fluid containing sulphocyanic acid in a combination which easily yields the acid when required. Such is the theory at present suggested.

I am not unaware of the difficulties in the way of its acceptance. The colour of hæmatin cannot, it is said, depend upon the iron it contains, because nearly the whole of the iron may be removed without affecting the colour of the hæmatin*. But it is not stated that all the iron is ever removed, and it may be that a very small proportion suffices for the formation of the colour, while the larger proportion of the metal is held in reserve in the globules in the same manner as sulphocyanic acid appears to be in the

serum.

Having found a sulphocyanide in the blood, it next occurred to me to look for it in the eggs of birds. It is natural to suppose that, since in the process of incubation red blood is formed, its assumed elements of colour would be found in the egg before incubation. This supposition proved correct. Fortunately the albumen of the hen's egg affords a ready means of research. It is only necessary to mix it with an equal quantity of distilled water, by which complete coagulation by the iron solution is prevented. The albumen of a hen's egg weighs about 300 grains, and this quantity was found to contain of a grain of sulphocyanic acid. The yolk was intimately mixed with water, then evaporated to dryness in the water-bath, and extracted with alcohol; but no trace of the salt could be detected. It is probable, therefore, that the sulphocyanide exists exclusively in the * Elements of Chemistry. By W. Miller, M.D., 3rd edit. p. 872.

albumen, which, as the process of vivification proceeds, enters into combination with iron, which originally exists in the yolk.

The presence of a sulphocyanide in saliva must be referred to one of two sources. It is either an exclusive product of the secretion itself, or it previously exists in the blood and is extracted from it as a component of the saliva. The amount of sulphocyanide found in different analyses varies greatly; my own results show only about half a grain in twenty ounces of saliva from a healthy subject. This nearly agrees with the observations of Bidder and Schmidt. Wright makes the quantity very much greater. If we take the estimate at only half a grain in twenty ounces of saliva, and reckon this to be the quantity of the secretion swallowed in twenty-four hours, the salt might be probably found in the blood and in the urine.

If, however, my experiments have been rightly interpreted, it is certain that sulphocyanide of potassium or sodium is not a mere product of the salivary glands, We have seen that it is found in the blood of all orders of vertebrate animals, and we know that fish do not possess salivary organs. Assuming that it is extracted out of the blood, what is its use in the saliva?

Considering its composition, it seemed possible that it acted either as an antiseptic or else as an agent which prevented fermentation in the alimentary canal, and thus indirectly aided digestion.

The conditions which favour the fermentation of saccharine matter, namely, acidity and the proper temperature, are constantly present in the stomach. Is sulphocyanide of potassium in saliva destined to check this fermentation, which, under favourable circumstances, may occur in less than an hour?

Carefully conducted experiments proved that it neither possesses the power of preventing ordinary fermentation nor that of checking it when already in action.

We shall now see what is its action in preventing putrefaction. Two equal portions of roast mutton were placed, the one in water, and the other in the same quantity of a solution of sulphocyanide of potassium of the strength of 1 grain of the salt to 1 ounce of water. After some weeks the meat which had lain in water was found to be broken up into shreds, and was quite putrid; that in the sulphocyanide solution was

merely softened, and had a sour smell, but was not putrid.

Sulphocyanide of potassium, therefore, possesses an antiseptic power; but whether or not this property comes into operation in the alimentary canal is a question I cannot now decide.

I have made many quantitative analyses to determine the amount of sulphocyanide eliminated with the urine in various diseases, including typhus, typhoid, and scarlet fever.

Not to enter into details at present, it will be sufficient to state what the results showed with much uniformity. In all diseases in which wasting of the body was marked, the excretion in the urine of a sulpho

cyanide, in common with some other substances, was unusually great. This increase of it in the urine was found to correspond with its decrease in, or more frequently its disappearance from, the saliva. This circumstance goes to prove that the salt is not formed by the saliva, but is an ingredient of the blood itself.

XIV. "On some Elementary Principles in Animal Mechanics."No. II. By the Rev. SAMUEL HAUGHTON, M.D. Dublin, D.C.L. Oxon., Fellow of Trinity College, Dublin. Received June 14, 1869.

In a former communication to the Royal Society on this subject (Proceedings, 20th June 1867), I endeavoured to establish the two following principles :

I. That the force of a muscle is proportional to the area of its cross section.

II. That the force of a muscle is proportional to the cross section of the tendon that conveys its influence to a distant point.

The first of these principles is true under all circumstances, but the second requires to be modified somewhat in its statement. If the conditions as to friction of the tendons that convey the action of the muscles to a distant point be the same, then the force of the muscles will be proportional to the cross sections of the tendons; but if the tendons be subjected to different amounts of friction, then the areas of their cross sections will cease to be proportional to the forces of the muscles, as represented by the areas of their cross sections.

In my former paper (No. I.), I selected, in illustration of principle II., the long flexor tendons of the toes of the Rhea and other struthious birds, and showed that the cross sections of the muscles and tendons bore, approximately, a constant ratio to each other. Now, in the Struthionidæ, the conditions as to friction of the long flexor tendons of the toes are similar although different in each species, and hence it was easy to prove that the ratios of the cross sections of the muscles and tendons were nearly constant.

When, however, muscles and tendons, variously conditioned as to friction, are compared together, the constancy of the ratio of their cross sections disappears, and undergoes a variation depending on the friction to which both muscles and tendons are exposed.

In order to ascertain the proportion of the cross section (or force) of a muscle to the cross section (or strength) of its tendon in the human subject, I made the following observations on the right arm and hand of a well-developed male subject in the Royal College of Surgeons in Ireland, in March 1868.

I first ascertained the specific gravities of the muscles and tendons, with the following results:

From these specific gravities it was easy to determine the cross section of either muscles or tendons, by weighing a known length of either one or other. In this manner the following Table was constructed :

Cross sections of Muscles and Tendons in an Adult Human Male Subject, and Ratios of same.

From the preceding Table, it appears that the ratio of the cross section of the muscles to that of the tendons may range from 7 to 28, or be four times greater in one case than another. We may also see in general, that the tendons exposed to the greatest amount of friction have the smallest coefficients of cross section. Thus the radial tendon of the biceps has a coefficient of 282, while the scapular tendon, which undergoes the friction of passing over the head of the humerus, has a coefficient of 18.0. Again, the Ext. oss. met. poll., whose tendon winds round the radius, and has the duty imposed upon it of binding down the tendons of the radial extensors of the wrist, has the coefficient of 77, as compared with 26.2 and 18.4, the coefficients of the comparatively free tendons of these extensors.

As it might be objected that the relative cross sections of muscle and tendon, in a human subject that died a natural death, might be exceptional

in character, from wasting during the last illness, I determined to test the question by experiment, and accordingly selected a fine Pyrenean Mastiff for the purpose, which I killed by strychnia, and dissected immediately after death, with the following results, which were obtained, as before, by noting the specific gravities of the muscles and tendons, and by weighing a measured length of each :--

Cross sections of Muscles and Tendons in a Pyrenean Mastiff, and ratios

These results, obtained from measurements made upon a freshly killed animal, confirm those found from observation of the human subject, and prove that the ratio of the cross section of the muscle to that of its tendon depends upon the amount of friction experienced by the latter, the coefficient being greater in proportion as the friction is less.

The following observations, made upon a Wallaby Kangaroo, confirm in a general way the preceding results:

Cross sections of Muscles and Tendons in a Wallaby Kangaroo, and ratios

It appears from the preceding investigation that the cross section of a muscle does not bear a constant ratio to the cross section of its tendon, unless the friction experienced by the muscle and tendon be also constant, and that there may even be a surplusage of strength in the tendon beyond what is absolutely necessary to resist the combined force of the muscle and friction. This surplusage, however, cannot be supposed to be large, if the principle of economy of material in nature be admitted.