II] THE LEAST OF ORGANISMS 41 



and therefore (taking its density as equal to that of water), a 

 weight of 



18 X 10-4 X 10-9 == 18 X 10-13 mgm. 



But of this total weight, the sulphur represents only 



18 X 10-13 X 15 X 10-5 = 27 X lO-i^ mgm. 



And if we divide this by the weight of an atom of sulphur, we have 



27 X 10-17 ^ 275 X 10-22 _ io,000, or thereby. 



According to this estimate, then, our little Micrococcus frogrediens 

 should contain only about 10,000 atoms of sulphur, an element 

 indispensable to its protoplasmic constitution ; and it follows that 

 an organism of one-tenth the diameter of our micrococcus would 

 only contain 10 sulphur-atoms, and therefore only ten chemical 

 "molecules" or units of protoplasm! 



It may be open to doubt whether the presence of sulphur be 

 really essential to the constitution of the proteid or " protoplasmic " 

 molecule ; but Errera gives us yet another illustration of a 

 similar kind, which is free from this objection or dubiety. The 

 molecule of albumin, as is generally agreed, can scarcely be less 

 than a thousand times the size of that of such an element as 

 sulphur: according to one particular determination*, serum 

 albumin has a constitution corresponding to a molecular weight 

 of 10,166, and even this may be far short of the true complexity 

 of a typical albuminoid molecule. The weight of such a molecule is 

 8-6 X 10166 X 10-22 _ 8-7 x lO-i^ mgm. 



Now the bacteria contain about 14 % of albuminoids, these 

 constituting by far the greater part of the dry residue; and 

 therefore (from equation (5)), the weight of albumin in our micro- 

 coccus is about 



^ij^ X 18 X 10-13 _ 2-5 X 10-13 i^gii^_ 



If we divide this weight by that which we have arrived at as the 

 weight of an albumin molecule, we have 



2-5 X 10-13 ^ 8-7 X 10-18 = 2-9 x 10*, 



in other w^ords, our micrococcus apparently contains something 

 less than 30,000 molecules of albumin. 



* F. Hofmeister, quoted in Cohnheim's Chemie der Eiweisskorper, 1900, p. 18. 



