350 Bulletin 167 



most of the field studies were conducted. The sap was collected 

 in clean tin buckets provided with japanned covers. The spouts 

 used were of galvanized iron. Care was exercised to keep the 

 buckets clean and sweet in order to avoid an accumulation of 

 micro-organisms in the sap. The sap was gathered in clean tin 

 cans such as are usually employed for transporting milk, and 

 carried to the farm house in which the temporary laboratory 

 was then established. It was divided into portions of sixteen 

 quarts each and placed in new tin buckets provided with covers. 

 Certain portions were reserved as controls and the remainder 

 were inoculated by adding 70 cc. of a young actively growing 

 culture of the specific organism selected. The controls were 

 treated with similar amounts of sterile culture media. The in- 

 oculated samples were placed on a table and incubated for three 

 days. The temperature variation during the respective incuba- 

 tion periods is shown in the accompanying graphs taken from 

 the tracings made by a self-recording thermometer placed near 

 the samples. The actual temperature of the sap was of course 

 much more constant than that of the air. After an incubation 

 period the various portions were made into sirup, each of the 

 several saps being evaporated in a bright sugaring-off pan on 

 a kitchen stove until condensed to a volume of about one quart. 

 It was then transferred to a white, agate-ware basin, and evap- 

 orated as rapidly as possible until the proper concentration, as 

 indicated by a thermometer, was reached. The process from 

 cold sap to sirup, required about an hour and a half for its 

 completion, except in the case of one sample when the time 

 was intentionally prolonged. The samples made during the first 

 season are those discussed in bulletin 151 as numbers 1 to 26 

 inclusive. The numbers used at that time, however, have not 

 been retained in the present publication. Moreover the method 

 of scoring employed in this article is not the one used in the 

 former issue, a fact which explains any apparent lack of uni- 

 formity. The numbers used in the present bulletin and in the 

 former one are given below in tabular form : 



