PREFACE TO THE SEVENTH EDITION. 



IN this edition pp. 17-18, 49-52, 103-104, 165-168, that is, the matter pertain- 

 ing to numerical aperture, refraction, the filar micrometer, imbedding 



and sectioning by the paraffin method, have been rewritten. Some errors are 

 noted, and additional or more advantageous methods suggested for some of 

 the sections. The title page has been slightly altered in wording to make it more 

 fully indicate the aim of the book. 



Ithaca, Jan. 11, 1899. 



Corrections. — Pp. 33, 39, 46, for Pleurasigma, read Pleurosigma. P. 97, second 

 paragraph, change No. 4 to No. 3. P. 159, top line, change carbol-xylene to 

 castor-xylene. 



Additions. — P. 145, (j 227 : If the proportions of acid and dichromate are 

 greater, this cleaning mixture will be more efficient. The following from Dr. G. 

 C. Caldwell's laboratory guide is excellent. Potassium dichromate 40 grams : 

 w T ater 150 c.c. ; sulphuric acid 230 c.c. For preparing this mixture, an iron kettle 

 lined with heavy sheet lead has proved both satisfactory and economical. 



Pp. 154, 177, ''/A 245, 308. Formaldehyde dissociator of the strength of 2 c.c. of 

 formalin, etc., to the liter, has been found more satisfactory than 5 c.c. to the 

 liter. 



Pp. 160, 166, Vi 261, 275. As pointed out in 1891 (Proceed. Amer. Micr. Soc, 

 Vol. xiii, p. 82) it is of great advantage to albumenize the slides on which collo- 

 dion sections are to be mounted. This is done by placing the cleaned slides in a 

 jar of egg albumen 1 to 200 of water. This should be filtered before use. After 

 half an hour or more the slides are removed, stood 011 end on a towel or blotting 

 paper and allowed to dry ; they can then be stored in glass jars and are ready to 

 use at any time. From such albumenized slides the collodion sections, fastened 

 as directed in <: 261, will very rarely become detached even with repeated manipu- 

 lation. Such albumenized slides are excellent for use with paraffin sections. If 

 the sections are to be extended with warm water ( \ 274) this is a much preferable 

 method to that with Mayer's albumen. 



P. 160, \\ 257-259. When objects are imbedded in a box for collodion sections 

 they must ordinarily be fixed to some holder before sectioning. After the collo- 

 dion is hardened in chloroform and clarified, remove the paper box, absorb the 

 castor-xylene on the surface, trim the end and put some fresh, thick collodion on 

 the cork or other holder. Press the imbedded tissue firmly against the holder. 

 Within two minutes it will be firmly cemented and one may proceed at once to 

 clamp the holder in the microtome and commence cirtting. 



