370 



NATURE 



[Aug. 31, 1876 



a suspicion as to the reason of this connection, and 

 a flood of light, therefore, broke on the subject the 

 moment he proclaimed the new physiological fact. Still 

 more Mitchell showed that the cataract he was able to 

 induce by experiment was curable also by experiment, a 

 truth which will one day lead to the cure of cataract with- 

 out operation. Then, but not till then, the splendid 

 character of this original investigation, and the debt that 

 is due to one of the most original, honest, laborious 

 workers that ever in any age cultivated the science and 

 art of medicine, will be duly recognised. 



When the news of Mitchell's discovery reached us here, 

 I took up the investigation at the point where he had 

 left it. The fact he had announced was found to be in- 

 disputable. From a patient in one of our large hospitals, 

 who was suffering from diabetes and double cataract, a 

 specimen of the sugar excreted was obtained, and from that 

 specimen the cataractous disease was induced in the frog, 

 and afterwards removed. The experiment was con- 

 ducted with the animal kept in an aneesthetic atmosphere, 

 and was found to answer just as well as in the ordinary 

 atmosphere ; in fact, the experiment succeeded best with 

 frogs when it was rendered free of all pain, as spas- 

 modic movements, which may occur if the process of pro- 

 duction of cataract is rapid, and which may suddenly kill, 

 are prevented. Since the introduction of chloral hydrate, 

 that anaesthetic has become a still more useful agent in 

 this research, since its own action runs in line with 

 the experiment, and the ansesthetic can be introduced 

 in actual combination with the substance producing the 

 cataract. 



In warm-blooded animals I learned that the cataractous 

 change could be brought about immediately after death. 

 Several of the experiments were made therefore on the 

 head of the sheep after the animal had been killed at the 

 slaughter-house in the ordinary way, the fluid being in- 

 jected through an artery. In other warm bloods the 

 death was first induced by one of the anaesthetic vapours, 

 and the fluid used was either injected into the peritoneal 

 cavity or through the aorta. 



The line of research which I carried on in continua- 

 tion of Dr. Mitchell's discovery was for the purpose 

 of determining the cause of the cataractous change and 

 the influence of other agents in producing it. It occurred 

 to me that the change was possibly due to the influence 

 of saline matter on the pure colloidal lens, and if this were 

 true the cataract ought to be induced by other substances 

 than sugar. Any of the soluble crystalloids might pro- 

 duce it, and as there are many of these in the blood, there 

 might be other cataracts than such as are produced by 

 sugar in the diabetic subject. The research was therefore 

 pursued with all the soluble salts belonging to the blood, 

 and with the result of producing cataractous change with 

 them all. In the end it was deduced that whenever the 

 specific gravity of the blood is raised, by the presence of 

 saline matter in it, to 10 degrees above the normal standard, 

 and is sustained in that state for a short time, cataract is 

 the result, and is maintained so long as the blood con- 

 tinues of the same specific weight. It was also found 

 that the cataractous condition caused by the soluble blood 

 salts was removable on the elimination of the added 

 saline and the reduction of the blood to its natural equi- 

 librium. At the same tiine there was observed to be a 

 difference in the characters of the cataracts produced. 

 Some of the saline cataracts were harder than the sugar 

 cataracts and less easily curable. Those salts which are 

 most fixed in their chemical constitution and at the same 

 time are most soluble, produce the hardest cataracts. 

 Those salts which are most easily decomposed, such as 

 urea, are least effective in inducing the pathological 

 change. 



The change was found to commence, as a rule, in the 

 posterior part of the lens, and after beginning as an im- 

 perfectly defined hazy spot it extended gradually through 



the whole structure, causing a pearly whiteness and com- 

 plete opacity. In the process of cleaning of the lens the 

 posterior part was the last to become transparent, but 

 without exception the whole structure of the lens regained 

 its crystalline clearness and its perfect function when the 

 specific weight of the blood was reduced to its natural 

 standard, if the circulation of fluid through the lens con- 

 tinued. 



In these experiments two illustrious scholars, now lost 

 to science, took the warmest interest, the late Pro- 

 fessor Graham and the late Sir David Brewster. Both 

 lent to me their valued observation. Graham saw in the 

 experimental facts the first application in physiological 

 pathology of his great discovery of the mutual action of 

 colloidal and crystalloidal substances. Sir David drew 

 some most ingenious inferences as to the physical cause 

 of the opacity, tracing it to a process of crenation on the 

 margins of the fibres of the lens. The greatest interest 

 was naturally excited throughout the medical profession. 

 In this production of cataract the first visible demon- 

 stration was offered of the synthesis of a well-known 

 disease. It is now certain that if the specific gravity of 

 the blood be raised rapidly a few degrees by a crystal- 

 loidal substance, cataract is the direct result. Recently 

 Dr. Sansom saw this event in the case of a young woman 

 suffering from diabetes, who became, in a few days, stone 

 blind from cataract in both eyes ; and, indeed, the cause 

 of diabetic cataract is now made quite plain. But the 

 end of the discovery is not reached with this fact, im- 

 portant though it be. The mode of production, in man 

 and the lower animals, of the slowly advancing cataract, 

 from which so many persons are rendered permanently 

 blind, is after the same process, with a different saline, 

 acting in a slower degree ; and the inference is fair that 

 some particular forms of diet are conducive to the disease. 

 When the whole series of facts which Mitchell com- 

 menced to unfold are completed, the disease cataract 

 will be understood in full. Its physical pathology is 

 already understood, and if the operative art of the sur- 

 geon be not quenched by another mode of cure resulting 

 from his discovery, it will be by the better art of preven- 

 tion of the disease. 



Experimentation on Pectons Changes. 



The observations on cataract above described led me 

 to follow out other lines of inquiry in respect to the action 

 of saline substances on living and dead colloidal matter. 

 I thus found that when a saline solution of a colloid, 

 such as albumen, is brought into contact with a living 

 colloidal structure like the peritoneum, the saline solvent 

 is rapidly removed into the circulation, and the colloidal 

 plastic substance is left on the true membrane as a false 

 membrane, by which contiguous membranes are agglu- 

 tinated together. I found further that if the blood 

 or serous part of the blood in a fluid saline condition 

 exudes into a serous cavity, the same simple physical pro- 

 cess goes on, the saline and watery parts, including the 

 colouring matter of the blood, passes back into the circu- 

 lation through the membrane and the colloidal fibrine 

 and albumen are left in form of false membrane or of 

 band, on the true membrane. The experiment illustrates 

 how inflammatory exudations, as they are called, are pro- 

 duced, and how adhesions and adhesive constrictions are 

 formed after inflammatory serous diseases. The experi- 

 ments on animals by which these results were arrived at, 

 were all conducted under anaesthesia, and were perfectly 

 painless. 



In another analogous series of inquiries conducted in 

 the same manner, I found that if the blood were sur- 

 charged with urea, a portion of albumen would pass out 

 of the body by the urinary secretion without the institu- 

 tion of any marked morbid change in the structure of the 

 kidney. This fact led me to ask whether albumen diluted 

 with water and charged with urea would pass through a 



