TOMATO KETCHUP UNDER THE MICROSCOPE. 3 



to occur. In some other cases the spoilage is due principally to 

 yeasts, and again bacteria may be the chief source of trouble. Then 

 again any two or all three forms of organisms may be present. 



Some manufacturers have supposed that the boiling incident to 

 manufacturing ketchup removed these organisms and the products 

 of decomposition from the material. But this is far from true; for 

 although they may be killed so that further spoilage due to them will 

 not occur, the forms are still readily seen by the aid of the compound 

 microscope, and by chemical methods it has been shown that some 

 of the most important products of the decay remain and the food 

 value of the product is irreparably injured. 



METHODS OF MICRO-ANALYSIS AND INTERPRETATION OF 



RESULTS. 



The methods used for determining the character of a pulp or 

 ketchup are given, since inquiries are repeatedly received for this 

 information. Unfortunately they are of such a character that the 

 manufacturer without scientific training can not use therii to any 

 great extent, though with practice a layman might be able to judge 

 roughly in some particulars as to the character of the product. 



APPARATUS REQUIRED. 



The outfit used is as follows : 



A good compound microscope giving magnifications of approxi- 

 mately 90, 180, and 500 diameters. This is accomplished by the use 

 of a 16 mm (two-thirds of an inch) objective and an 8 mm (one- 

 third of an inch) objective, together with a medium (X6 compen- 

 sating) and also a high-power ocular (X18 compensating). A 

 Thoma-Zeiss blood-counting cell, 1 a 50 cc graduated cylinder, and 

 ordinary slides and cover glasses complete the apparatus required. 

 It is impractical to use objectives of a higher power than those men- 

 tioned, because of their short working distance, which makes their 

 use with the counting cell impossible. 



ESTIMATION OF MOLDS. 



A drop of the product to be examined is placed on a microscope 

 slide and a cover glass is placed over it and pressed down till a film of 

 t he product about 0.1 mm thick is obtained. After some experience this 

 <-an be done fairly well. A film much thicker than this is too dense 

 to be examined successfully, while a much thinner film necessitates 



1 This is a cell named after the designer of the form of rulings used, and consists of a 

 slide with a disk ruled in one-twentieth mm squares, so arranged that when the cover '.& 

 in place the film of liquid under examination is one-tenth mm deep. They were orig- 

 inally intended for counting corpuscles in the blood and are obtainable from practically 

 all manufacturers of microscopic accessories. 



