RELATION TO INFECTIOUS DISEASES. 99 



servation will be needed before he can tell where and when 

 this bird is accustomed to build its nest, upon what insects, 

 grains, and berries it feeds, with what other species of birds 

 it lives in peace and with what it is at war. A much 

 greater range of observation and study is necessary before 

 the naturalist can tell how his newly discovered species 

 would thrive if carried to a new climate, where it would 

 be compelled to live upon unaccustomed food, to build its 

 nest of strange material, and to encounter new foes. 



We repeat that it is no discredit to the srience nor to the 

 men who have developed it to say that the study of bac- 

 teriology has hitherto been almost wholly morphological. 

 Without the morphologist the physiologist and the physio- 

 logical chemist could not exist. The science having had 

 for its support only raorphological studies, the deductions 

 and formulated statements arrived at by its students have 

 been reached in accordance with the knowledge obtained 

 from this source. But now, it being admitted that the 

 causal relation between a given germ and a certain disease 

 is dependent upon the chemical products of the growth of 

 the germ, the fundamental lines of work must be altered in 

 order to correspond witli this new knowledge. 



The study of the chemical factors in the causation of the 

 infectious diseases opens up for us a field in which much 

 Avork must be done. Let us attempt a statement of the 

 nature of some of the researches that must be carried out 

 along this line. 



In the first place, we must ascertain what germs are toxi- 

 cogenic. This would necessitate a chemical study of all kinds 

 of bacteria, both the pathogenic and the non-pathogenic. 

 Every fact ascertained in this investigation will not have 

 its practical application in medicine, but will have its 

 scientific value, and many will most probably be of more 

 or less direct service to man. 



Secondly, it must be determined under what conditions 

 these germs are toxicogenii-. It is not at all probable that all 

 those bacteria which are capable of producing poisons when 

 grown on dead material outside of the body are also capable 

 of multiplication and the production of the same substances 



