520 FOOD PRESERVATION 
Bitting (1915) have also stated that the method is unsatisfactory. 
Indefinite directions are especially mentioned. Vincent (1918) has 
maintained the above objections. Bitting and Bitting have pointed 
out the practical impossibility of concentrating tomato pulp to the 
consistence of tomato paste and having it pass the standard of 25,000,- 
000. The inadequacies of the procedure are soon apparent to anyone 
who attempted to use the method. The difficulty of distinguishing 
between particles of organic matter and bacteria makesthe results very 
uncertain. These criticisms caused a restatement of the procedure. 
More definite details have been given by Howard (1917) as follows: 
Howarp’s Revisep Mertrsop ror THE MICROANALYSIS OF TOMATO 
PrRopucts 
Apparatus. (a) Compound Microscope. Equipped with apochro- 
matic objectives and compensating oculars, giving magnifications of 
approximately 90, 180 and 500 diameters. These magnifications can 
be obtained by the use of 16 and 8 mm. Zeiss apochromatic objectives 
with X6 and X18 Zeiss compensating oculars, or their equivalents. 
such as the Spencer 16 and 8 mm. apochromatic objectives with Spencer 
X10 and X20 compensating oculars, the draw tube of the microscope 
being adjusted as directed below. 
(b) Thoma-Zeiss Blood-counting Cell.* 
(c) Howard Mounting Cell. Constructed like a blood-counting cell 
but with the inner disk (which need not be ruled) about 19 mm. in 
diameter. 
Molds (Tentative). Clean the Howard cell so that the Newton’s 
rings are produced between the slide and the cover glass. Remove the 
cover and place by means of a knife blade or scalpel, a small drop of the 
sample of the central disk; spread the drop evenly over the disk and 
cover with the cover glass so as to give an even spread to the material. 
It is of the utmost importance that the drop be mixed thoroughly and 
spread evenly; otherwise the insoluble matter and the molds are most 
abundant at the center of the drop. Squeezing out of the more liquid 
portions around the margin must be avoided. In a satisfactory mount, 
Newton’s rings should be apparent when finally mounted and none of 
the liquid should be drawn across the moat and under the cover glass. 
*Comment by the authors. In using these cells the plane parallel cover glasses 
furnished with them should be used instead of the ordinary microscope cover glasses. 
Since the latter are subject to curvatures that introduce errors in the thickness of 
the mounts. 
