40 MORPHOLOGIC VARIATION 



both cultures were equally and simultaneously seeded. He con- 

 cludes, therefore, that there is a toxic substance which is adsorbed 

 by the filter, but that after a certain period of filtration the filter 

 becomes saturated and allows the substance to pass through. This 

 experiment, like the filtration experiment of Chesney, is very sug- 

 gestive, but cannot be considered conclusive until it has been re- 

 peated a sufficient number of times to show that it is universally true. 



With the relatively recent discovery of the bacteriophage, the 

 question has naturally arisen whether or not these supposed auto- 

 toxic substances formed in cultures of bacteria might not be the 

 d'Herelle principle. Hajos says that the inhibitory products of 

 metabolism which he obtained from exhausted cultures have nothing 

 in common with the bacteriophage. Otto and Munter, apparently 

 accepting as valid Conradi and Kurpjuweit's autotoxine, showed that 

 the latter was not neutralized by antilysin. Kauffman, denying the 

 existence of the autotoxine, naturally concludes that it is not identi- 

 cal with the lytic substance of d'Herelle. 



While many of the experiments reported above are very sug- 

 gestive of the occurrence of toxic products which tend to limit growth, 

 and one cannot, therefore, categorically deny their existence, there 

 is nowhere any clearcut evidence that such substances are universally 

 formed, sufficient to warrant the prevalent acceptance of the idea. 

 The observations of Penfold and Norris, Salter, and Graham-Smith 

 with bacteria, of Brown, Zikes and Montank with yeasts, that the 

 rate of growth and the final yield are proportional to the concen- 

 tration of nutrient in the medium, seem to offer a serious obstacle 

 to the toxic theory, for it seems more likely that toxic products of 

 growth would accumulate more rapidly and thus inhibit growth 

 sooner with a medium of higher nutrient value, rather than the re- 

 verse. The crucial experiments of Graham-Smith, in which he 

 showed that a culture of staphylococci could be revived at any time 

 after the maximum growth period and caused to grow again by 

 simply adding some more meat extract in concentrated form, and 

 that the death phase could be postponed indefinitely by small daily 

 additions of meat extract, would seem sufficient to completely upset 

 the toxic theory, unless one can believe that meat extract is an anti- 

 dote to the autotoxine! 



