620 



LABORATORY EXERCISES 



When It is intended to sow a definite number of cells,i water is usually added to 

 the yeast to be used as sowing material, the cells being thus more easily separated 

 from one another on shaking; also, no appreciable increase of the cells takes place, 

 especially if the flask is subjected to a low temperature after the sample has been 

 withdrawn. 



Fig. 2i8A. — Blood counter case, a, Slide with counting chamber; b, rubber cork 

 covering tip of white pipette; c, soft rubber tubing; d, red pipette provided with 

 rubber cork; e, cutting needle in 95 percent, alcohol; g, Hayem's' solution; h, .5 per 

 cent, acetic acid. {After McJunkin.) 



The yeast is, therefore, shaken up vigorously and continuously with sterile water, 

 and an average sample removed. There are three different cases to be considered 

 now viz.: (i) When we wish to know only how many cells are present in a certain 

 portion of the water-yeast mixture; (2) when it is intended to inoculate a previously 

 determined number of cells into the liquid to be dealt with; and (3) when it is desired 

 to sow so many cells, that after the seeding the definite number of cells desired may 

 be present in an arbitrary space unit, e.g., when making comparisons of the multiply- 



1 Klocker, Alb.: Fermentation Organisms, 1903. 



