534 THE MEASUREMENT OF BACTERIA, 



lengths varying between the normal length of a mature cell and 

 twice that length when the cell is about to divide into two 

 individuals. Small bacteria may even appear less than the 

 normal when they are lying in the film at an angle with the 

 coverglass. It is of greater consequence to have a correct 

 estimation of the breadth of bacteria, and especially the breadth 

 in relation to the normal length, for then we can have a true 

 picture of the organism. .Small differences in breadth influence 

 the general appearance of the cells to a greater degree than small 

 differences in length. This can be clearly seen by comparing the 

 two figures, in one of which (fig. 1) the diagrammatic bacteria 

 have a constant breadth and varying length, and in the other 

 (fig. 2) they have a constant length and varying breadth. 



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Since, owing to the method of reproduction of the fission fungi, 

 the breadth is more constant than the length, all suggestions for 

 arriving at a truer approximation of the breadth than can be 

 made by estimating it directly' with the micrometer eyepiece, 

 should be welcomed. Means other than the convenient micro- 

 meter eyepiece have been advised. Wright* proposed to project 

 the image of a scale or of a system of squares upon the plane 

 upon which the microscopic objects are disposed. Wilson and 

 Randolph! photograph the bacteria at a magnification of 1000 

 diameters. They also photograph a ruled system of squares so 

 that the rulings are exactly one millimetre apart. Then by 



* Journ. Eoy. Microscop. Soc, 1897, 182. 

 t Journ. Applied Microscopy, 1899, 598. 



