/ J-O w — 



vii 



strivings between rival destructive and preservative tendencies sup- 

 posed to be resident in the body itself, but in the existence in its 

 environment of elements injurious to its welfare. 



At an earlier period, the absence of physical and chemical know- 

 ledge would have rendered the success of any such attempt impossible. 

 As it was it was imperfect and was recognised as such by its author ; 

 but it was so unquestionably the beginning of that rapid development, 

 by which, under the influence of Virchow and his pupils, what we 

 now recognise as the science of pathology has come into existence, 

 that of this science Henle must be regarded as the founder. 



In certain directions, indeed, Henle was in advance of his successors. 

 If, for example, we take the opening chapter of the u Untersuchungen," 

 which deals with the etiology of contagious diseases, we find in it a 

 most remarkable anticipation of the discoveries in this field of inquiry 

 of the last fifteen years. He sets forth in the clearest language that 

 the material of contagium mast necessarily be not only organic but 

 living and organised, and that it must consist of "parasitical beings 

 which are certainly among the lowliest, smallest, but at the same 

 time most productive which are known." 



The consideration of the reasoning which led Henle to this con- 

 clusion, affords a striking illustration of the way in which discoveries 

 made in other departments of natural science influence medicine. 

 Henle's grounds were* (1) the evidence of experiments that contagion 

 acts in infinitesimal quantities, and must therefore be self-multiplying; 

 (2) the proof then shortly before given by Schwann that the analogous 

 processes of fermentation and putrefaction are dependent on minute 

 organisms : (3) the proof recently given by Basse tt Audouin that the 

 muscardin of silkworms, a disease communicable through the air, 

 was due to a contagium vivum ; and finally (4), the consideration that 

 the development of contagious diseases could be best explained by 

 attributing them to a living cause. 



That Henle did not himself follow these indications may probably 

 be attributed to his being engrossed by other researches. It seems at 

 first sight difficult to account for the fact that the seed sown by him 

 did not fructify in the minds of some of his readers ; for when in 

 1868 the investigations of Chauveau again brought the subject of 

 contagium vivum to the front, it was approached from au entirely 

 different point of view. 



A sketch must be given, in conclusion, of the views which Henle 

 entertained and taught as to the psychological side of biology. 

 Mention has already been made of his having lectured at Heidelberg 

 on anthropology. These lectures were given to a mixed academical 



* See his " Pathologische Untersuchungen," Berlin, 1840, pp. 17 — 20, and 

 36—41. The publication of this work was preparatory to that of the "Rationelle 

 Pathologic" 



