1885.] 



MICEOSCOPICAL JOUKNAL. 



177 



It is unfortunate that • no more 

 deaths from this sickness have oc- 

 curred.' A portion of the meat 

 should have been fed to the doctors 

 before thev hatl an opportimity to re- 

 port on it. 



The journal of the American 

 Medical Association contains another 

 account of the poisonous beef, where- 

 in it is stated that a severe form of 

 cholera morbus occurred in Momence. 

 Illinois, on July 17th. due to the eat- 

 ing of decomposed dried beef. About 

 fortv persons were aflected. The 

 jfonrnal reprints the reports of Drs. 

 Utley and Ellis, and adds that 'Dr. 

 Kevser. on microscopical examina- 

 tion with 600 diameters, found nu- 

 merous animalcuhe.' which is 

 likewise a highly instructive state- 

 ment for a professional gentleman to 

 make ! 



Prof. G. A. Mariner found numer- 

 ous micrococci, bacilli, and other 

 bacteria, so it appears that in spite of 

 the reports of the other gentlemen 

 there really was something the matter 

 with the meat. 



Testing Objectives. — Not im- 

 frequently w^e are asked by persons 

 v^ishing to purchase objectives, to ad- 

 vise them what kind they should get, 

 and if we will test the lenses before 

 thev are selected. It is not a difficult 

 matter for one familiar with micro- 

 scopic work to select a good objective 

 for every-day use. There is a vast 

 amount of humbug talked about this 

 matter by persons who ought to "know 

 better. Perhaps, after all, it is mostly 

 for effect upon the novice^ who, no 

 doubt, is inspired with envv for the 

 person whose long experience enables 

 him to subject an objective to various 

 • tests' to determine what it will do. 

 But the fact is. as every practical ob- 

 server well knows, the best test for 

 a working objective is to use it in reg- 

 ular work for a short time. It is well 

 to have also a good Podura scale, 

 which is an excellent object to show 

 the character of the definition. 



When we come to a different class 



of lenses, of vcr}- large angular aper- 

 ture, such as are now much in demand 

 by amateurs who can afford them, and 

 by others who must have them, the 

 tlifHculties are somewhat greater. It 

 is customary to try such lenses upon 

 a test-plate, and report how many of 

 the diatoms it resolves. Unfortu- 

 nately, this is a very misleading test. 

 It will do very well for those who de- 

 sire a lens for such work alone ; but 

 for most other purposes it is not a test 

 in any sense. 



In this case also the most satisfac- 

 tory test for the lens is j^ractical use 

 in the work to be done with it. Many 

 an observer of unquestionable skill 

 in microscopical examination would 

 be utterly ' at sea ' if asked to resolve 

 the Aviphiplchra . Yet we are in- 

 clined to believe such an obsen'er is 

 quite as well qualified to pass judg- 

 ment upon an objective as any other. 



There is, however, one way of test- 

 ing an objective thoroughly, in every 

 particular, and that is by means of the 

 test-plate of Professor Abbe, made by 

 Mr. Zeiss. This test-plate deserves 

 to come into general use by those who 

 make a study of objectives. 



This subject was treated at length 

 some time ago by Dr. H. E. Fripp, 

 and we can do no better than to use 

 his words in conclusion. He says :* 



• In ordinary practice, microscope 

 objectives, if tested at all by their 

 possessors, are simply subjected to a 

 comparison of performance with other 

 lenses tried upon the same '• test ob- 

 jects." The relative excellence of the 

 image seen through each lens may, 

 however, depend in a great part upon 

 fortunate illumination, and not a little 

 upon the experience and manipulative 

 skill of the observer ; besides which 

 any trustworthy estimate of the per- 

 formance of the lens under examina- 

 tion involves the consideration of a 

 suitable test-object, as well as the 

 magnifying power and aperture of the 

 objective. The structure of the test- 

 object should be well known, and the 

 value of its '■ markings," if intended 



*yourn. R. Micr. Soc, ser. 2, vol. iii, p. 120. 



