Cut along, running to secure a treatment for blood (9)
I believe the answer is:
coagulant
'treatment for blood' is the definition.
(substance causing blood to coagulate)
'cut along running to secure a' is the wordplay.
'running' indicates anagramming the letters.
'to secure' indicates putting letters inside (inserted letters are secured inside).
'cut'+'along'='cutalong'
'cutalong' with letters rearranged gives 'coagulnt'.
'coagulnt' enclosing 'a' is 'COAGULANT'.
(Other definitions for coagulant that I've seen before include "Substance that aids clotting" , "What provokes clot" , "It enables clot" , "clotting agent" , "it produces clots" .)