THE STUDY OF GLYCOLS IN TISSUES 93 



groups, to form aldehyde groups which may then be detected 

 with the aldehyde reagents. Hotchkiss has shown that treat- 

 ment with periodate may be a very valuable procedure in the 

 study of carbohydrates in tissues, provided that the carbohy- 

 drates are insoluble in water (see, for example, Plate XII, Fig. 

 B) . This technique has at present been far less extensively ex- 

 ploited than is desirable. There is a possibility that it could be 

 used to demonstrate the presence of pentose nucleic acid. Nor- 

 mally a nucleic acid does not contain an a,/?-glycol grouping. 

 After hydrolysis of pentose nucleic acid, as in the Feulgen pro- 

 cedure, an extra hydroxy group is liberated on Ci by the re- 

 moval of the purine moiety from the nucleic acid. Consequently 

 if there is also a free hydroxyl group on C 2 , the compound now 

 contains an a,£-glycol group which should be susceptible to oxi- 

 dation by periodate. In the case of the thymonucleic acid C 2 

 does not bear an hydroxyl group, unlike pentose nucleic acid. It 

 is not at present known, however, whether the hydroxy group at 

 C 2 is normally phosphorylated in pentose nucleic acid. If it is 

 not, after a Feulgen-type hydrolysis, pentose nucleic acid should 

 contain a glycol grouping which can react with periodate. 



An attempt has been made to study the distribution of a sub- 

 stance with the above structure in tissues, using the following 

 procedures : 



1. The tissue is embedded in wax, one result of which is to remove any 

 fatty aldehyde which may be present. 



2. It is necessary to remove any preformed glycol grouping. This is 

 quite readily done by treatment with periodate which transforms the gly- 

 col groups into aldehyde groupings. These groups are later (in Step 4) 

 blocked with hydroxylamine or dimedone. 



3. Sections are submitted to a Feulgen hydrolysis in the presence of 

 mercury. The hydrolysis splits off purine. The mercury prevents 

 nucleic acid from going into solution. 



4. As a result of the Feulgen hydrolysis reactive aldehyde groups are 

 liberated on the deoxy sugars but not on the normal sugars. This reactive 

 aldehyde, together with that formed in Step 2, is blocked by treatment 

 with hydroxylamine or dimedone. 



5. The sections are then treated with periodate to oxidize any a,/3-glycols 

 liberated in Step 3 to aldehyde groups. 



6. The section is exposed to reduced fuchsin to colour the sites of alde- 

 hyde groups. 



When this procedure is carried out it has been found that with 

 a number of tissues, e.g., pancreas, a colour appears in those sites 



