July 28, 1916] 



SCIENCE 



115 



eases known as infectious, and imniimology 

 to utilize these discoveries in the specific 

 prevention and cure of many of them. The 

 infectious diseases are not only important 

 in themselves, but are recognized as in- 

 directly the cause of many of the chronic 

 diseases, so called, which are slower in 

 their course, but none the less health- 

 destroying and fatal in their outcome. The 

 growth of bacteriology has been coincident 

 with the filling of the ranks of our present 

 army of laboratory workers, many of whom 

 have been primarily concerned in advancing 

 this science. Bacteriology owes its stable 

 beginnings to two men, Louis Pasteur, a 

 chemist, and Robert Koch, for a brief time 

 a country physician and later professor of 

 hygiene in Berlin. Immunology, the sci- 

 ence which explains natural protection to 

 infectious disease and utilizes this knowl- 

 edge in creating such conditions artificially, 

 we owe first after Pasteur to Metchnikoff, 

 a Polish biologist with no exact medical 

 training. It is characteristic of these sci- 

 ences that their problems, although arising 

 in cases of human and animal disease, have 

 been developed, in large part, away from 

 the bedside, under the conditions of greater 

 accuracy and completeness afforded by the 

 experimental reproduction of the disease in 

 animals. Such an experimental disease 

 may be interrupted and attentively studied 

 in its successive stages and its course may 

 often be followed outside the animal body 

 under conditions of greatest clearness. 



It was the great service of Pasteur, and 

 particularly of Koch, to show that each one 

 of an increasing number of infectious dis- 

 eases is caused by a separate and identifi- 

 able type of microorganism. Such a micro- 

 organism is always found in each case of 

 the disease in question, but in no other in- 

 stance, and will give rise again to the same 

 disease when reintroduced in a healthy . 

 animal of the same species. The first in- 



stances of infectious diseases studied, an- 

 thrax, typhoid, chicken cholera, tubercu- 

 losis, and others, were found to be due to 

 minute plants called bacteria. Later ob- 

 servers have described similar infectious 

 diseases due to equally lowly animal para- 

 sites, particularly to those known as pro- 

 tozoa. 



Typhoid fever was one of the first of the 

 human infectious diseases to yield the 

 secret of its parasitic cause. The typhoid 

 bacillus, B. typhosus, was first described by 

 Carl Joseph Eberth in 1880, who found it 

 microscopically in tissues from a patient 

 that had died of typhoid fever. It was 

 grown outside the body in pure culture four 

 years later by George Gaffky. This organ- 

 ism was soon recognized as the cause of 

 typhoid fever, although the final postulate 

 necessary to prove the etiological relation- 

 ship to the disease was not fulfilled until 

 1900, when Metchnikoff and Besredka suc- 

 ceeded in producing the disease experimen- 

 tally with pure cultures in anthropoid apes. 

 Of great corroborative importance in prov- 

 ing the causative relationship of the typhoid 

 bacillus was its presence in the stools and 

 urine of cases of typhoid fever, which was 

 demonstrated in 1885. In the same year 

 Fraenkel and Simmonds found the micro- 

 organism in the circulating blood of a case 

 of typhoid fever, a condition which was 

 later shown by the work of Kiihnan (1897), 

 Castellani and Schottmiiller to be fairly 

 constant during early stages of the malady. 

 This observation not only proved finally 

 and conclusively the etiological relation of 

 the typhoid bacillus to typhoid fever, but 

 led to a gradual reconstruction of our con- 

 ception of the disease itself so that we have 

 finally come to regard it primarily as a 

 septicemia or blood infection rather than an 

 intestinal disease per se, as the striking 

 lesions in the small bowel had led us to 

 assume. 



