8 . Introduction. 



parts of the body is interfered with, fails or becomes irregular, 

 as in case of cardiac obstruction, obstruction of the blood vessels 

 or intestinal canal by clots of blood or foreign bodies, or how in- 

 testinal displacement or unusual taxing of the organs must or 

 may lead to disturbances. The entire group of physiological 

 methods of investigation are of value in the solution of pathological 

 problems ; physics and chemistry aid in explanation and find the 

 most varied application in their study. There has been developed 

 in pathology along the lines of its special studies a series of prac- 

 tical methods of animal experimentation, known as Experimental 

 Pathology, affording accurate information in many of the problems 

 of pathogenesis and supplying valuable demonstrations of the cor- 

 rectness of our best established observations and conclusions. One 

 may at will, by operative procedure upon living animals, by ligation 

 or occlusion of blood vessels or ducts of glands, produce and imitate 

 mechanical changes of various types ; and it is quite possible by 

 killing the experiment animal at any time to note precisely the 

 anatomical changes and progress of the disease thus induced, from 

 which the course of actual diseases of a corresponding type have 

 come to be well appreciated. By operative removal of some organ 

 or part of an organ, it is possible to obtain an idea as to the results 

 which are likely to follow analogous disease processes in the same 

 part, as in case of the thyroid gland, liver, kidney or adrenal. All 

 our knowledge of regenerative growth of tissues, the healing of 

 wounds, the union of fractured bodies and of the general process of 

 inflammation we owe directly to experimental studies on animals. 

 By administering to animals various types of material of ap- 

 parently poisonous character, it has been possible to study the action 

 of a wide range of substances and to acquire the essential basis 

 for diagnosis of the intoxications. The complete life history of the 

 animal parasites, their development and multiplication in the human 

 and animal body, and the diseases caused by them, have been worked 

 out by means of animal experimentation in a really classical man- 

 ner; and the practical application of this knowledge in food exami- 

 nation, in meat inspection and in other lines of prophylaxis against 

 disease, are exceedingly numerous and have led to marked diminu- 

 tion of such diseases as hydatids, trichinosis and mange. But above 

 all else animal experimentation has lifted the dark cloud which 

 formerly obscured the nature of infectious diseases; and only from 

 successful attempts in transmission by inoculation has it been pos- 

 sible to explain and obtain precise knowledge as to the real nature 



