RECENT ADVANCES IN SCIENCE BEARING ON MEDICINE. 575 



existence of free cell formation, which really implied the revival of the 

 old doctrine of spontaneous generation. This belief was gradually- 

 driven out of the domain of zoology, but in connection with the forma- 

 tion of plastic exudates found a sanctuary in that of pathology. I 

 myself was taught the discontinuity of pathological growths — a view 

 which would logically lead back to the origin of living from nonliving 

 matter. But enlightenment in this matter came to me. At the end of 

 my academical career I was acting as clinical assistant in the eye 

 department of the Berlin Hospital, and I was struck by the fact that 

 keratitis and corneal wounds healed without the appearance of plastic 

 exudation, and I was thus led to study the process of inflammation in 

 other nonvascular structures, such as articular cartilages and the intima 

 of the larger vessels. In no one of these cases was plastic exudation 

 found, but in all of them were changes in the tissue cells. Turning- 

 next to vascular organs, and in particular those which are the common 

 seats of exudation processes, I succeeded in demonstrating that the 

 presence of cells in inflammatory exudates was not the result of exuda- 

 tion, but of multiplication of preexisting cells. Extending this to the 

 growth in thickness of the long bones — which was ascribed by Duhamel 

 to organization of a nutritious juice exuded by the periosteal vessels — 

 I was thus eventually able to extend the biological doctrine of omnis 

 cellula e cellula to pathological processes as well; every new formation 

 presupposing a matrix or tissue from which its cells arise and the 

 stanrp of which they bear. 



HEREDITY. 



Herein also lies the key to the mystery of heredity. The humoral 

 theory attributed this to the blood, and based the most fantastic ideas 

 upon this hypothesis. We know now that the cells are the factors of 

 the inherited properties, the sources of the germs of new tissues and 

 the motive power of vital action. It must not, however, be supposed 

 that all the problems of heredity have thus been solved. Thus, for 

 instance, a general explanation of theromorphism, or the appearance 

 of variations recalling the lower animals, is still to be found. Each 

 case must be studied on its merits, and an endeavor made to discover 

 whether it arose by atavism or by hereditary transmission of an acquired 

 condition. As to the occurrence of the latter mode of origin, I can 

 express myself positively. Equally difficult is the question of heredi- 

 tary diseases; this is now generally assumed to depend on the trans- 

 mission of a predisposition which is present, though not recognizable, 

 in the earliest cells, being derived from the paternal or maternal tissues. 

 But the most elaborately constructed doctrines as to the hereditariness 

 of a given disorder may break down before the discovery of an actual 

 causa viva. A notable example of this is found in the case of leprosy, 



