LETTER 26. 27 SEPTEMBER 1678 181 
grass, I observed that they came not out of the air (as 
was the vulgar opinion), but out of the grass itself: the 
cause whereof I conceived to be this. The dry cold, that 
we had some three weeks earlier, caused the death of the 
extreme tips of some blades of grass; and this was followed 
by very warm weather, which drove fresh nourishment 
again upwards through the pores’ in the grass. But this 
food-matter, wherewith the pores of the grass were filled, 
being unable to get out at the top (because the ends or 
the uppermost pores of the grass were stiff and dried up), 
burst open the pores in many places where they were 
most weakened ; and thus many globules were squeezed 
out of them. These globules, lying stuck together upon 
the outside of the grass, and becoming stiffer on exposure 
to the surrounding air, took upon themselves a reddish 
colour; whereas these same globules, when they le in- 
closed in the pores, are green.” And whenever one 
happens to strike one’s foot against such grass, the said 
globules are dusted off it, and make one’s shoes reddish. 
But since a red colour is most agreeable with the notion 
of fire, we must not take it amiss in the common man if 
he deems the said substance to be a fiery matter: seeing 
that there are among us physicians (who fancy themselves 
experienced) who say, when they see blood whose whey- 
like matter * is yellow, that the blood is bilious; or say of 
black blood, that ’tis burnt: just as if everything yellow 
were bile; and everything black, burnt.’ 
Meantime the Fellows of the Royal Society’ had not been 
wholly idle in the matter of the “little animals.” Robert 
* Port MS. 
> L. evidently confused the red corpuscles on the grass-blades with 
chloroplasts within them. 
* i.e, serum. 
* It is clear from this, and many another passage in L.’s writings, that 
he had but a poor opinion of the general medical practitioner of his day. 
*> The Fellows (or some of them) would perhaps have taken particular 
interest in the observations on infusions: for they would recall—unlike 
