266 Scientific Proceedings (116). 



media. Twenty per cent, horse serum gives practically constant 

 titres at some time during the growth. The time relationships 

 hold in all concentrations. Peptone (2 per cent.) slightly in- 

 creases the titre and gives identical titres in 20 per cent, horse 

 serum, and brings the variations within closer limits in rabbit 

 serum media. The time relationships are directly dependent on 

 the growth of the streptococci, so that the delay in lysin production 

 in horse serum indicates a lag in the rate of multiplication during 

 the early hours after seeding. Variations in the nature of the 

 seeding can be obviated by seeding from a 20 per cent, horse 

 serum broth in 2 per cent, peptone, in which all streptococci of 

 human origin, whether virulent or avirulent, reach the same con- 

 dition in regard to growth and number at the end of 16 hours, 

 unless agglutination occurs. 



135 (1717) 



The failure of rats to develop rickets on a diet 

 deficient in Vitamine A. 



By A. F. HESS, G. F. McCANN and A. M. PAPPENHEIMER. 



[From the Department of Pathology, College of 

 Physicians and Surgeons, New York.] 



The fat-soluble vitamine, or a vitamine closely associated with 

 it, is regarded by some as being equivalent to an antirachitic 

 vitamine; the development or non-development of rickets is 

 thought to be dependent mainly on the absence or presence of 

 this factor. In a previous report one of the writers has stated it 

 to be his opinion that this relationship does not hold true for 

 human rickets. The following experiments were planned to 

 ascertain whether a diet markedly deficient in this vitamine led 

 to the development of rachitic lesions in young rats; for this pur- 

 pose rats weighing about 30 g. were put on a diet of extracted 

 casein 21 per cent., rice starch 57 per cent., salt mixture 5 per cent., 

 Crisco 17 per cent., yeast extract (Osborne and Wakeman) 60 

 mg. a day. The casein was extracted by means of ether and 



