800 



SCIENCE 



[N. S. Vol. XXVIII. No. 727 



better known to medical men than to micro- 

 scopists, using the latter term in its more 

 restricted sense. 



As his work, especially upon the " opsonins," 

 has been so largely dependent upon the aid of 

 the microscope he came naturally to appre- 

 ciate that instrument and to realize the need 

 of a thorough understanding of its possibili- 

 ties and limitations for the investigator who 

 must enlist its help in his researches. 



The keynote of the work is struck in the 

 opening paragraphs of the preface : 



Every one who has to use the microscope must 

 decide for himself as to whether he will do so 

 in accordance with a system of rule of thumb, 

 or whether he will seek to supersede this by a 

 system of reasoned action based upon a study of 

 his instrument and a consideration of the scien- 

 tific principles of microscopical technique. 



The present text-book has no message to those 

 who are content to follow a system of rule of 

 thumb, and to eke this out by blind trial and 

 error. 



It addresses itself to those who are dissatisfied 

 with the results thus obtained, and who desire to 

 master the scientific principles of microscopy, even 

 at the price of some intellectual effort. 



The book in carrying out the plan just indi- 

 cated deals with the microscope itself. It is 

 not a work upon animal or vegetable histol- 

 ogy with just enough about the microscope 

 to enable the student to know which end of 

 the instrument to look into, and with this to 

 expect the student to elucidate all the complex 

 structure of animal or plant. 



Part I., included in the first 48 pages, deals 

 with what the author calls the " stage pic- 

 ture," that is, the object and its illumination. 

 It is shown by abundant and easily performed 

 experiments just what it is necessary to do to 

 prepare and illuminate objects so that they 

 may be visible with the microscope by the so- 

 called dark outline (refraction image) or by 

 coloration (color image). In forecasting the 

 future with respect to the discovery of the 

 causes of diseases such as scarlatina, measles 

 and many other human and animal diseases, 

 he controverts the assumption made by many 

 that the organisms, if they exist at all, are of 

 " ultra-microscopic minuteness " and adds : 



This failure appeals only as an illustration of 

 the rule that micro-organisms (with rare excep- 

 tions) remain for all practical purposes invisible 

 and unidentifiable in the interior of the organism 

 until methods of differential staining are discov- 

 ered which allow of their representation in the 

 stage picture. If we have here, as the present 

 writer believes, the true explanation of the ill 

 success of the bacteriological microscopist in the 

 matter of the discovery of the germs of the dis- 

 eases specified above, that discovery can not be 

 expected until further progress shall have been 

 made in those comparatively unregarded, but in 

 reality fundamentally important, chemical re- 

 searches which lead up to the invention of new 

 processes of differential staining. 



In Part II., including about 190 pages, the 

 author takes up the formation of images by 

 the microscope and the function of each one 

 of the optical parts or elements involved. 



In the first place it is shovm that a simple 

 aperture may form an image and that the 

 inversion of the image and the magnification 

 are the same as when a lens is used; but 

 while this is true he proceeds to illustrate, 

 again by abundant experiments, the difference 

 in clearness of the lens-formed image and that 

 of the simple aperture (pin-hole picture). 

 In this study there is shown with admirable 

 simplicity how to determine the aperture and 

 the significance of the same in image forma- 

 tion. 



The aberrations (spherical and chromatic) 

 of lenses are illustrated and the methods of 

 elimination discussed, as well as the effects 

 produced by diffraction. It seems to the re^ 

 viewer that the question of diffraction in 

 microscopic vision receives in this work the 

 most lucid treatment on record; and going 

 with this is the most satisfactory discussion 

 of the relation of microscopic and naked-eye 

 vision. It must be confessed that for the 

 average worker with the microscope it is dis- 

 quieting to have it impressed upon him that 

 microscopic vision is totally unlike naked-eye 

 vision, as is done in many works and papers 

 upon the subject. Just where the break comes 

 in between naked-eye vision and that with 

 spectacles, the simple or the compound micro- 

 scope, no one has determined. That diffrac-- 



