CAUSATION OF DISEASE 307 



fungous nature of favus, a scalp disease, was recognized by 

 Schonlein in 1839, and the organism was afterward called 

 Achorion schoenleinii. Berg, in 1839-1841, showed that 

 thrush is likewise due to a fungus, O'idium albicans. 



These discoveries led Henle in 1840 to publish a work in 

 which he maintained that all contagious diseases must be 

 due to living organisms, and to propound certain postulates 

 (afterward restated by Koch and now known as "Koch's 

 postulates," page 229) which must be demonstrated before 

 one can be sure that a given organism is the specific cause 

 of a given disease. The methods then in vogue and the in- 

 struments of that period did not enable Henle to prove his 

 claims, but he must be given the credit for establishing the 

 "contagium vivum" theory on a good basis and pointing 

 the way for men better equipped to prove its soundness in 

 after years. 



In 1842-1843, Gruby showed that herpes tonsurans, a form 

 of ringworm, is due to the fungus Trichophyton tonsurans. 

 Klencke, in 1843, produced generalized tuberculosis in a 

 rabbit by injecting tuberculous material into a vein in the 

 ear, but did not carry his researches further. In 1843, 

 Dr. Oliver Wendell Holmes wrote a paper in which he 

 contended that puerperal fever was contagious. Liebert 

 identified the Peronospora infestajis as the cause of one type 

 of potato rot in 1845. The skin disease pityriasis (tinea) 

 versicolor was shown to be due to the Microsporon furfur 

 by Eichstedt in 1846. In 1847, Semmelweiss, of Vienna, 

 recommended disinfection of the hands with chloride of 

 lime by obstetricians because he believed with Holmes in 

 the transmissibility of puerperal fever through poisons car- 

 ried in this way from the dissecting room, but his theories 

 were ridiculed. 



Pollender, in 1849, and Davaine and Rayer, in 1850, inde- 

 pendently observed small rod-like bodies in the blood of 

 sheep and cattle which had died of splenic fever (anthrax). 

 That Egyptian chlorosis, afterward identified with Old 

 World "hookworm disease," is caused by the Anhjlostoma 

 duodenale was shown by Griesinger in 1851. In the same 

 year the Schistosomum hematohium was shown to be the 



