4 ELEMENTARY BIOLOGY. [CHAP. 



will be found that they are giving rise to minute buds, which 

 rapidly grow, assume the size of the parent Torula^ and 

 eventually become detached ; though, generally, not until 

 they have developed other buds, and these yet others. The 

 Torulcc thus produced by gemmation, one from the other, 

 are apt long to adhere together, and thus the heaps and 

 strings mentioned, as ordinarily occurring in yeast, are pro- 

 duced. No Torula arises except as the progeny of another; 

 but, under certain circumstances, multiplication may take 

 place in another way. The Torula does not throw out a bud, 

 but its protoplasm divides into (usually) four masses, termed 

 ascospores, each of which surrounds itself with a cell-wall, 

 and the whole are set free by the dissolution of the cell- 

 wall of the parent. This is multiplication by endogenous 

 division. 



As each of the many millions of Torulcz which may thus 

 be produced from one Torula has the same composition as 

 the original progenitor, it follows that a quantity of Protein, 

 Cellulose and Fat proportional to the number of Torula 

 thus generated, must have been produced in the course of 

 the operation. Now these products have been manufactured 

 by the Torulce out of the substances contained in the fluid 

 in which they float and which constitute their food. 



To prove this it is necessary that this fluid should have 

 a definite composition. Several fluids will answer the pur- 

 pose, but one of the simplest (Pasteur's solution) is the 

 following. 



Water (H 2 O). 



Sugar (C ]9 H M O n ). 



Ammonium Tartrate (C 4 H 4 (NH 4 ) a O 6 ). 



Potassium Phosphate (KH 2 PO 4 ). 



Calcium Phosphate (Ca 3 P 2 O 8 ). 



Magnesium Sulphate (MgSOJ. 



