914 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



on one edge of a glass cover resting upon a smooth surface, and to 

 draw the end of a glass slide, held obliquely, across the face of the 

 cover. No pressure must be used, or the delicate corpuscles will be 

 crushed and distorted. 



In selecting a field for photography, the aim should be to obtain 

 one in which the circular form of the red corpuscles is preserved, in 

 which they do not overlie each other, and in which one or more white 

 corpuscles are to be seen. Unfortunately, an ideal field is hard to 

 find, and the patience of the operator will often be sorely tried in the 

 effort to find one. 



The white corpuscles being larger than the red, and spherical in 

 form, are very commonly drawn to the edge of the stain in the opera- 

 tion of spreading. Care must be taken that the blood-stain is quite 

 dry and the circle of cement upon which the cover is to be mounted 

 quite hard, before it is placed in position on the slide ; for moisture, 

 or chloroform from the cement, would injure the preparation. 



A series of photo-micrographs of blood-corpuscles, made with a 

 standard amplification, would not only be interesting and instructive, 

 but might also be useful for reference, to those who are called upon 

 to examine blood-stains for the purpose of giving expert medico-legal 

 testimony. 



The photographic method would also be useful for recording 

 differences in the form and appearance of blood-corpuscles due to 

 disease, if any constant peculiarities of this kind were associated with 

 particular diseases. But the Microscope does not reveal any such 

 peculiarities of a sufficiently definite character to justify the expecta- 

 tion, at one time extensively entertained, that its use, in the examina- 

 tion of the vital fluid, might prove of value in deciding questions of 

 diagnosis. Differences in the relative proportion of the white and 

 red corpuscles are, however, shown in a rough way, and the depth of 

 colour of the red corpuscles is indicated, to a certain extent, by the 

 photographic contrast with the ground; or, better still, with white 

 corpuscles in the same field. The presence of foreign elements — 

 parasitic organisms — ^is shown very satisfactorily in photographs ; 

 and if a sufficient power is used, their absence is rendered apparent 

 when there are none. 



The method is therefore especially useful for recording facts of 

 this kind, as the observer is able to substantiate the truth of his state- 

 ments, positive or negative, by unimpeachable evidence, and at the 

 same time to show that his skill as a microscopist is sufficient to give 

 confidence in his ability to manipulate the higher powers with which 

 Bucb observations are necessarily made. 



For example, the photo-micrograph of yellow-fever blood given by 

 the author, in which the amplification is nearly 1500, and in which 

 the white and red corpuscles are well defined, may be taken as 

 evidence that there were no parasites in the blood of the patient from 

 whom this specimen was obtained ; and a sufficient number of similar 

 photo-micrographs of blood from different patients, and drawn at 

 different stages of the disease in question, would prove the absence of 

 any foreign elements, demonstrable with the power used, from the 



