115 
Ckumability  of  Cream. 
Photographic  Examination. 
This  part  of  the  investigation  has  been  considerably  devel- 
oped. Last  year  photographs  were  taken  of  thin  films  of 
milk  of  unknown  thickness  (see  page  37  et  seq.  of  Journal 
R.A.S.E.,  Yol.  70).  This  year,  however,  by  using  a specially 
constructed  glass  cell,  it  was  found  feasible  to  ensure  that 
all  the  photographs  obtained  were  of  films  of  milk  of 
which  the  thickness  was  known.  Thus,  with  a known 
thickness  or  depth  of  milk,  it  was  possible,  by  counting 
and  measuring  the  globules,  to  ascertain  the  volume  of  milk 
arid  the  proportion  of  fat  it  contained,  in  any  part  shown  in 
the  micro-photograph.  The  figures  so  obtained,  when  com- 
pared with  the  results  given  by  analysis,  afford  a very  valuable 
check.  The  comparisons  are  shown  in  the  following  state- 
ment : — 
Number  of  globules  counted 
11m 
10m 
9m 
8/* 
7m 
6m 
5 M 
4m 
3m 
2m 
lM 
16.  Shorthorn  . 
— 
1 
— 
1 
5 
10 
29 
97 
213 
295 
456 
17.  South  Devon 
- 
- 
- 
- 
2 
20 
45 
184 
403 
500 
757 
18.  Jersey  . 
- 
- 
1 
6 
26 
44 
65 
160 
211 
199 
432 
19.  Red  Poll 
1 
1 
1 
— 
15 
41 
57 
155 
255 
423 
601 
Percentage  of  fat  (by  volume  i in  each  size 
globule 
Total  per- 
centage of 
fat  (by 
volume) 
.2  •“.a 
73 
o +- 
3 
>»  r 
11m 
10m 
9m 
8^ 
7m 
6/a 
6m 
4m 
2m 
lM 
d w -jr 
££  £ 
p“  ° 
-d  cu 
CJ  •_ 
p 
16.  Shorthorn  . 
— 
•087 
— 
■045 
150 
188 
•316 
•542 
•502 
•206 
•040 
2076 
1'874 
2'60 
17.  South  Devon 
- 
- 
- 
- 
•060 
•377 
•491 
1'028 
■950 
•349 
■066 
3 321 
2 995 
364 
18.  Jersey  . 
- 
- 
•064 
•268 
■778 
•829 
•709 
•893 
•495 
•139 
038 
4213 
3800 
3-83 
19.  Red  Poll 
•116 
•087 
■064 
- 
•449 
•773 
•622 
•866 
■601 
•295 
•052 
3925 
3541 
3'28 
It  must  be  pointed  out  that  in  calculating  from  the  very 
small  portion  of  the  film  of  milk  visible  under  high 
magnification,  it  was  necessary  to  multiply  by  1666  to  get  the 
result  in  the  case  of  a cubic  millimetre  even.  Consequently, 
the  very  slightest  error  made  in  measuring  the  micro-photo- 
graph is  multiplied  over  sixteen  hundred  fold.  Hence  the 
agreement  between  the  figures  obtained  from  the  photographic 
method  of  examination,  and  those  obtained  by  chemical  analysis, 
shows  that  the  photographs  taken  under  the  new  system  are 
fair  representations  of  the  milk  examined.  It  is  interesting 
to  note  that  the  average  error  made  in  the  measurements  of 
