A further explanation of the reason why jaundice occurs in an epidemic form, may be found in the circumstance that in all febrile states of the general system some one or other of the internal organs is liable to become congested. For example, typhus is, as a rule, complicated with cerebral congestion, typhoid with mesenteric, ague with splenic, scarlatina with renal, and so on. It is not, however, necessary that the organs should be affected in the same relation to the disease as is here given. On the contrary, in one epidemic of typhus, the brain may be congested, in another the lungs, and in a third the liver; and so also with other fevers. Hence we can have little difficulty in understanding why epidemics of jaundice every now and then occur, seeing that they are but the secondary results of other epidemic affections, although, as occasionally happens, the jaundice is the chief, if not the only well-marked symptom. ARTIFICIAL JAUNDICE. What is the source of the tyrosine, and leucine found in the urine, in cases like those previously described? Being well aware that the physiologist {96} has it in his power to produce almost any pathological state or artificial disease at pleasure, I set about imitating on an animal the effects produced in the human subject by obstruction of the bile-ducts. Hitherto, artificial jaundice has been usually induced either by ligaturing the gall-ducts or injecting bile into the circulation; but as both of these methods were in the present instance objectionable--the first on account of the constitutional disturbance liable to be induced by the severity of the operation; the second from the bile being all at once thrown into the circulation, and thereby producing toxic effects, besides the danger of its too rapid elimination by the urine--I adopted another plan, which came much nearer to the state induced by disease in man--I took the bile of three healthy dogs, and injected it under the skin of a fourth. In this case the effects of the operation were almost _nil_, and the bile was at the same time placed in a position favourable for its slow absorption, just as in the human subject. During the first two days the animal remained comparatively well, the urine was normal in appearance, and contained neither bile-pigment, nor bile-acids. But on the third day the animal became ill, and on the fourth jaundice set in. He died on the fifth. After death the urine was found to contain not only {97} bile-pigment, and bile-acids, but also the diseased products, leucine, and tyrosine; and what was more interesting still, the urine was loaded with sugar, just as occurred in the case imitated.