Generic Characters in the Coccaceae 



■?5 



extreme forms which show only packets. None of these differences 

 but that between the presence and absence of packets appear on 

 agar with sufficient constancy to be determined definitely. For 

 distinction between streptococci and micrococci the observation 

 of broth cultures would perhaps be valuable. 



Dimensions. — The cocci exhibit a range in size from o . i to 

 2.0 /i with considerable variation between individual cells in the 

 same culture. We were somewhat surprised to find that we could 

 demonstrate no definite relation between size and the age of cul- 

 tures, or the conditions of cultivation. In a series of preliminary 

 studies the same organism was grown on seven kinds of media and 

 examined at intervals during a period of two months. The maxi- 



120 



100 



JZA 



80 

 60 

 40 

 20 



.1 .2 .5 .4. .5 .6 .7 .8 .9 10 



Fio. I.— Dimensions of 345 cocci. Abscissae, average diameter in i^. Ordinates, number of cultures. 



mum size, in different cultures, was recorded on the first, second, 

 seventh, 14th, 42d days, and after two months respectively. The maxi- 

 mum size developing in the different kinds of media during those 

 two months was found, respectively, in broth at 37°, broth at 20°, 

 Nahrstoff-Heyden, nutrient gelatin, acid and alkaline gelatin, and 

 under anaerobic conditions. In other words, the age and kind of 

 medium had no constant effect, except that in most cases the Nahr 

 stoff and other poor media showed the smallest individuals. No 



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