Frost—Bacteriological Control of Public Milk Supplies. 1317 
clean and free from grease, since a definite volume is pushed, out. 
If some clings to the sides more will be pushed out in its stead. 
d) Ring Method (Schroeder). 
In regard to the ring method of securing small fractions of a 
c.c. of milk, Dr. M. C. Schroeder of the Eesearch Laboratories, 
Department of Health, New York City says: “It was found af¬ 
ter a number of experiments that a small % in. No. 20 japanned 
curtain ring would take up within 5% of 0.01 c.c. of milk, and 
by dropping this ring full of milk directly into the melted agar 
tube we could eliminate one or more of the dilution bottles and 
thus save labor and a possible source of error. The rings are 
dipped into the milk by means^f a platinum hook and dropped 
directly into about 8 c. c. of nutrient agar held in the tube. ’ ’— 
Schroeder.* 
An attempt has been made to determine the accuracy of these 
curtain rings as volumetric devices. This was done first by de¬ 
termining the weight of such rings before and after being filled 
with milk. Sensitive chemical balances were used. Several 
weighings follow: Two rings were balanced, then one of the 
pair was dipped in milk and weighed: 
1) Weight required to balance again. 0.008 gms. 
2) Weight required to balance again. 0.008 gms. 
In another series: 
8) Weight of ring and milk was found to be.054 gms. 
Weight of ring after washing and drying.044 gms. 
Weight of milk taken up.01 gms. 
4 ) Weight of ring with milk.054 gms. 
Weight of ring after washing and drying.043 gms. 
Weight of milk taken up.011 gms. 
Culture Tests. A Certified milk was used. After a very thor¬ 
ough shaking five rings were dipped into the milk and plated. 
Four of them were put into the Petri dish. The other one was 
dropped into the melted agar in the test-tube and then this tube 
of agar was poured. The results follow: 
1) Developed . 50 colonies 
2) Developed . 24 colonies 
3) Developed . 25 colonies 
4) Developed . 9 colonies 
5) (In test-tube) developed. 27 colonies 
* Jour. Infect. Dis., 1912, 11, p. 3. 
