290 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Suppose he now tries his lenses on a Microscope with a condenser. In 

 regard to his low-angled inch, he can find no difference as it was filled 

 before, but with his 1/4 the definition is worse, because he has brought 

 out the spherical aberration of his lens ; he therefore prefers the Micro- 

 scope without a condenser, and calls them a ' fad of English micro- 

 scopists.' Let him, however, view the same objects with similar lenses, 

 well corrected and of decent angles, properly illuminated by a condenser, 

 and his conversion will be complete. 



Thirdly, the object. There is a golden rule for microscopists which 

 has been so freqiiently stated that I would not repeat it were it not that 

 it is so frequently disregarded. It is this : ' Use as low a power as 

 possible.' 



The favourite procedure with histologists is to use a high power 

 uncritically where a low power used critically would be far better. 



I would greatly prefer to use a 4/10 of 80° with a 1 in. eye-piece 

 than a 1/6 of the same angle with a 2 in. eye-piece, both being used 

 with a condenser. What shall we say when a 4/10 of 80° with the 

 1 in. eye-piece is used with a condenser, and the 1/6 of 80° and 2 in. 

 eye-piece is used without ? 



I am firmly persuaded that we should hear far less of ' low-angled 

 glasses for penetration ' if powers suitable to the object were used. 



There are published microscopical works with diagrams stated to 

 have been drawn under the magnification of an oil-immersion 1/12, 

 which, as far as the detail in them is concerned, might have been drawn 

 with a 1/2 in. ; and yet such a thing calls forth no remark in the 

 microscopical world. . . . 



Let me append just two statements out of the many I have heard 

 from histologists themselves on this subject. ' We cannot see anything 

 like this with an oil-immersion 1/12.' The object in this case was 

 tubercle bacillus with a 1/2 in. A yonng graduate fresh from one of 

 the first laboratories in the kingdom remarked, ' We have nothing like 



this at .' Some anatomical subjects under a power of 140 with a 



4/10 of 80° called forth that statement. So much for the testimony of 

 others. I will now give two instances from my own experience. A 

 curved piece of pink-stained dirt about the size of a Motifer vulgaris was 

 shown to me for a comma bacillus. If a true comma bacillus had been 

 placed under that Microscope it would have been quite invisible. 



On another occasion I was shown S. anthrax under an oil-immersion 

 1/12 ; in this instance it was just possible to differentiate a something 

 out of the general smudge which might be said to resemble the object 

 when you knew what to look for. The exhibitor has public reputation 

 for microscopical knowledge. 



Fourthly, a histologist prefers his Microscope without a condenser, 

 because the condenser would accentuate the deplorable condition of his 

 fine-adjustment. A sharp critical image requires a precise focusing 

 apparatus, but an uncritical image, i. e. an image without an edge * to 

 it, can stand a jerky fine-adjustment. 



Fifthly, daylight. Bad as a Microscope without a condenser is, it be- 

 comes far worse when illuminated by artificial light instead of daylight. 



With lamplight a cone from the plane mirror becomes an impossi- 

 bility, so one has to be contented with the best that can be got (sometimes 



* An image in which the boundaries of the detail arc all fluff. 



