456 



8CIEN0E. 



LN. S. Vol. XI. No. 273. 



yellowest, on the other. At the same time, 

 by selecting the colony which liquefied 

 most rapidly and the one which liquefied 

 most slowly, he was able to obtain from the 

 same original culture, rapidly liquefying 

 cultures, and those with hardly any liquefy- 

 ing power. He raised the question whether 

 many of the changes which had been de- 

 scribed as due to changed environment, 

 might not really be due to such unconscious 

 diflferentiated selection. 



The significance of varieties among Pathogenic 

 Bacteria: Professor Theobald Smith. 

 In the study of bacteria, morphological 

 details are of but little value in dififerentia- 

 ting and classifying forms because of their 

 m.inuteness. Processes of conjugation and 

 other sexual phenomena, such as are found 

 among Protozoa, are unknown. 



The problem of variation may be dis- 

 cussed under these heads : 



1. The actual existence of bacteria whose 

 relationship is conceded, although they 

 manifest slight differences among them- 

 selves. 



2. The artificial modification of bacteria 

 by experiment. 



3. The evolution of parasitic from sapro- 

 phj'tic forms. 



In the investigation of problems of this 

 character it is necessary to study, not only 

 the effect of related bacteria on the same 

 host, but that of the same bacteria on dif- 

 ferent hosts. Our investigations should be 

 both experimental and comparative. 



(The variations occurring in the group of 

 bacteria of which the rabbit septicaemia 

 bacillus is the type, and those occurring in 

 thepathogenic derivatives of the colongroup, 

 were discussed and illustrated. Variations 

 among tubercle bacilli, in form and viru- 

 lence, and among diphtheria bacilli, in 

 the production of toxin, were also referred 

 to.) 



The modifications which bacteria under- 



go, during passages through animals, vary 

 in degree with the species and group under 

 observation ; with some, such as the rabbit 

 septicaemia bacilli, streptococci, and pneu- 

 mococcii increase in virulence is easily at- 

 tained ; with the colon group this is much 

 more difficult. The degree of change that 

 can be impressed upon any bacteria prob- 

 ably depends largely on the specific struc- 

 ture of the organism. 



The evolution of parasitic from sapro- 

 phytic forms is a very slow and gradual 

 process, whose mechanism may have dif- 

 fered with different species. Special ad- 

 vantages which a certain environment may 

 offer for frequent passages through suscep- 

 tible species may give certain saprophytes 

 an impulse towards a parasitic existence. In 

 any case, such saprophytes probably possess 

 from the outset certain fighting characters, 

 such as the power to produce toxins which 

 enable the few among the myriads of forms, 

 eventually, to become disease germs. (Pub- 

 lished in the Journal of the Boston Society of 

 Medical Sciences, January 16, 1900.) 



Methods employed in the teaching of Bacteri- 

 ology : Professor H. C. Ernst. 

 In response to a circular letter sent to 

 the Institutions of Learning that teach 

 medicine, as given in the 1899 volume of 

 Minerva, there were returned ninety-eight 

 replies. The letter asked for information 

 as to whether Bacteriology was taught as 

 a separate branch — in case it was not, in 

 what department it was included — how 

 many instructors were engaged in teaching 

 this subject — the hours required — and other 

 details of interest. It was found that forty- 

 two institutions give instruction in Bacteri- 

 ology as a separate department^twenty- 

 six give separate courses, in connection 

 with the department of Hygiene, and thirty- 

 seven in connection with the department 

 of Pathology, or Pathological Anatomy. 

 The increase in the numbers of teachers 



