EXPLANATION OF PLATES xvii 



Covers and slides in flint of 1-72 ; diatoms in a medium 2-4. 



We are bound, however, to note that the condenser used is not corrected in 

 any way ; its aberrations are enormous. Although the highest admiration must 

 be expressed for the skill exercised by Dr. van Heurck in these remarkable 

 photo-micrographs, and the highest esteem for his courtesy to the present Editor 

 in supplying them, it must not be forgotten that Dr. van Heurck was obliged 

 to employ an imperfect condenser a condenser absolutely unconnected and 

 although we can testify to the high quality and fine corrections of at least one 

 of the lenses of N.A. 1-6, we are convinced that much of its real perfection 

 in image-forming is destroyed by uncorrected sub-stage illumination. Upon 

 the corrections and large aplanatic a'rea presented by the condenser and its 

 careful and efficient employment depends entirely the nature of the image 

 presented by the finest objective ever constructed ; and as the perfection of the 

 objective, with a high amplification and a great aperture, is more nearly 

 approached, the more dependent are we upon perfect corrections in the con- 

 denser to bring out the perfect image-forming power of the objective. No 

 image formed by such an objective as that possessing N.A. 1-60 can be consi- 

 dered reliable until a condenser corrected for all aberrations like the objective 

 itself is produced ; and so convinced are we of the possible value of this objec- 

 tive that we trust its distinguished deviser and maker may be soon induced to 

 produce the condenser referred to. 



If, then, by the aid of the chemist we can discover media which will be 

 of sufficiently high refractive index, and still tolerant or non-injurious to 

 organic tissues immersed in it, a new line of investigation may be open to 

 histology and pathology. W. H. D. 



PLATE XII. (Facing p. 597) 

 ARACHNOIDISCUS jAPONicus. (After B. Beck) 



The specimens attached to the surface of a seaweed are represented as 

 seen under a th objective, with Lieberkiihn illumination : A, internal 

 surface ; B, external surface ; C, front view, showing incipient subdivision. 



PLATE XIII. (Facing p. 651) 



BACTERIA, SCHIZOMYCETES, OR FISSION FUNGI 



1. Cocci singly and varying in size. 2. Cocci in chains or rosaries (strepto- 

 coccus). 3. Cocci in a mass (staphylococcus). 4 and 5. Cocci in pairs 

 (diplococcus). 6. Cocci in groups of four (merismopedia). 7. Cocci in packets 

 (sarcina). 8. Bacterium termo. 9. Bacterium termo x 4000 (Ballinger and 

 Drysdale). 10. Bacterium septicamia hamorrhagica. 11. Bacterium pneu- 

 monia crouposa. 12. Bacillus subtilis. 13. Bacillus murisepticus. 14. 

 Bacillus diphtheria. 15. Bacillus typhcsus (Eberth). 16. Spirillum undula 

 (Cohn). 17. Spirillum volutans (Cohn). 18. Spirillum cholera Asiatics. 

 19. Spirillum Obermeieri (Koch). 20. Spirochceta plicatilis (Fliigge). 21. 

 Vibrio rugula (Prazmowski). 22. Cladothrix Forsteri (Cohn). 23. Cladothrix 

 dichotoma (Cohn). 24. Monas Okenii (Cohn). 25. Nonas Warmingii (Cohn). 

 26. Ehabdomonas rosea (Cohn). 27. Spore-formation (Bacillus alvei). 28. 

 Spore-formation (Bacillus anthracis}. 29. Spore-formation in bacilli cultivated 

 from a rotten melon (Frankel and Pfeiffer). 30. Spore-formation in bacilli 

 cultivated from earth (Frankel and Pfeiffer). 31. Involution-form of Crenothnx 

 (Zopf). 32. Involution-forms of Vibrio serpens (Warming). 33. Involution- 

 forms of Vibrio rugula (Warming). 34. Involution-forms of Clostridium 

 polymyxa (after Prazmowski). 35. Involution-forms of Spirillum cholera 

 Asiatica. 36. Involution-forms of Bacterium aceti (Zopf and Hansen). 

 37. Spirulina-form of Beggiatoa alba (Zopf). 3j3. Various thread-forms of 

 Bacterium mcrismopedioides (Zopf). 39. False-branching of Cladothrix (Zopf). 



