188 The Philippine Journal of Science i9i8 



This requires a little experience and some knack, which are soon 

 mastered. Investigators desiring to do embedding and section- 

 ing are advised to consult the standard works dealing with those 

 subjects. 



In handling rich cultures of the small amoeboid forms, such as 

 Vahlkampfia, a drop of the medium containing the amoebse may 

 be placed on the surface of the slide. If the slide be laid aside 

 in a moist chamber for a little while, the organisms will settle 

 on to the glass, extend their pseudopodia, and remain there. 

 The slide may be then immersed in the fixing fluid, when it will 

 be found that the amoebae will adhere firmly to the slide and vnW 

 remain there through the subsequent manipulations. Many 

 other small forms will do this — even some of the flagellates — 

 but the larger species, particularly the ciliates, will almost 

 always float off the slide and become lost. 



Measuring. — Ideally, measurements should be made of the 

 living organisms, but it is not always possible to do this because 

 of the movements of the organism. The animals should be killed 

 in a fluid that will not shrink, swell, or otherwise alter their form, 

 and they should not be subjected to pressure such as that of 

 the cover glass. Measurements of less than flve hundred indi- 

 viduals have no great value. Care should be taken not to 

 measure species outside of those it is desired to study, also to 

 measure individuals in the same phase of the life cycle. In 

 measuring small forms fixed on the slide, select only those that 

 lie perfectly parallel with the surface of the slide — that is to 

 say, do not measure the animal unless its entire surface is in 

 perfect focus at one time. 



Jennings " uses Worcester's fluid (saturated solution of mer- 

 curic chloride in 10 per cent formol, 9 parts ; acetic acid, 1 part) 

 or a chrome-osmic fluid made up in the proportion of 1 per 

 cent osmic acid in 1 per cent chromic acid for killing and fixa- 

 tion. The animals are brought in a drop of fluid medium into a 

 Syracuse watch glass and immediately overwhelmed with a large 

 volume of the killing fluid. A portion of the fluid is then re- 

 moved with a pipette, and 25 per cent glycerin is added, in which 

 the cells are kept until they have been measured. The actual 

 measurement is made with an Edinger drawing and projection 

 apparatus. The organisms are transferred to a thin slide on 

 a flat drop of the glycerin without a cover. They are then 

 projected on to a drawing board and drawn and measured with 



"Jennings, H. S., Assortative mating, variability and inheritance of 

 size, in the conjugation of Paramecium, Journ. Exp. Zool. (1911), 2, 1. 



