47 



a good preparation is to be preferred for this purpose to a poor one, that 

 oulj' the best obtainable is to be photographed at all; but we are now 

 in a position to photograph anj- object better than it is possible to see it 

 by any single focusing of the microscope, and bj^ repeated exposures any 

 object can be photographed as well as it can be seen, so that all at 

 least can be seen in the pictures that can be in the object. Fig. 7 is an 

 egg from the ovary of a cat; the section is so thick that tissue cells lying 

 behind it can be seen through it; and yet all is clear. It goes without 

 saying that all the figures of the accompanying plates are of considerable 

 thickness; one of them. Fig. 16, is an unsectioned blastula of Ascaris; 

 the cavity within is seen through a cell which lies above it, and the light 

 that illuminates it has passed through a cell that lies below, and yet 

 tlie blastocoele is produced with almost diagramatic clearness. 



WHAT THE NEXT STEP IN PHOTOMICROGRAPHY OUGHT TO BE. 



The apparatus for the best work in photomicrography is very ex- 

 pensive and always will be. It requires and always will require an expei't 

 knowledge to make lantern slides and prints from microscopic prepara- 

 tions that an investigator can not afford to acquire and keep, and time 

 that he could ill afford to spare. Education ought not to lack, it must 

 not, Avill not lack this means of furthering its ends. We must establish 

 here and there laboratories of photomicroscopy, in connection, preferably, 

 with some of our institutions of learning, at which this work can be done 

 for a considerable number of institutions. By this means negatives 

 would accumulate from year to year until thousands of them might be 

 at the command of all; the cost need not be great for all schools to possess 

 slides of their own from this collection, or slides might be rented at a very 

 small cost; all investigation monograms could thus be illustrated and 

 teaching everywhere could be put in almost immediate touch with the 

 latest that is known, and nothing else so vitalizes the work of the class- 

 room, as every one knows who has tried it. I have tried to get slides 

 from the plates used in works that had been published and copyrighted; 

 I have never been able to do so; there was perhaps no means by which 

 they could be easily made; there should be no other reason; they could 

 only be used for teaching purposes; when one has harvested all the honor 

 and money that can come from his publications I can not see why the 

 good, that it does not impoverish him to part with slinuld not be shared. 



